Investment Securities - Investment securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Available for sale securities:
Available for sale securities	$ 189,917	$ 256,268
Trading debt securities:
Trading debt securities	134,753	180,715
Equity securities:
Equity securities	184,987	214,176
Equity method securities:
Total investment securities	579,344	688,346
Commercial paper
Available for sale securities:
Available for sale securities	9,714	1,977
Trading debt securities:
Trading debt securities	18,774	1,977
Corporate bonds
Available for sale securities:
Available for sale securities	180,203	254,291
Trading debt securities:
Trading debt securities	70,984	84,920
U.S. treasury bills
Trading debt securities:
Trading debt securities		5,979
Mortgage-backed securities
Trading debt securities:
Trading debt securities	1	4
Term loans
Trading debt securities:
Trading debt securities	44,994	44,268
Consolidated Sponsored Funds
Trading debt securities:
Trading debt securities		43,567
Common Stock
Equity securities:
Equity securities	34,206	34,945
Sponsored funds
Equity securities:
Equity securities	149,857	178,386
Equity method securities:
Equity method securities	69,687	37,187
Sponsored privately offered funds
Equity securities:
Equity securities	$ 924	$ 845

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